1. Field of the Invention
This invention relates to heat transfer core for water cooling towers, and especially to film fill pack having so-called film fill sheet that brings heated water into contact with flowing air for an increased time to maximize cooling of the water.
In a water cooling tower, heated water enters the tower from a source. Such heated water may be a byproduct of a manufacturing process or of an environmental cooling system, such as an air conditioning or refrigeration system. Through use of airflow, the cooling tower transfers heat from the water to the atmosphere. The cooled water then returns to the source to remove more heat in a repeating cycle. Airflow in cooling towers has two forms: cross-flow and counter flow. Cross-flowing air passes substantially laterally across the flow of the heated water. Counter-flowing air moves substantially against the flow of the heated water. A film fill sheet may operate in both airflow, situations.
2. Description of the Related Art
For many years, water cooling towers had fill packs made of horizontal bars or slats upon which heated water was splashed or sprayed to form droplets. The droplets of heated water were exposed to air forced through the cooling tower to cool the droplets. By forming the droplets, the surface area of the water increased and thus enhanced the cooling effect on the water when exposed to the forced airflow through the cooling tower. In recent years, film fill packs containing vertically positioned, horizontally spaced synthetic resin sheets have replaced the splash bars. The film fill sheets disperse the heated water into a film of water exposed to the air stream thus increasing the surface area of the water over the droplets previously formed by the splash bars. The film fill sheets replaced splash bars because of their smaller size which in turn reduced the size of the cooling tower.
U.S. Pat. No. 4,801,410 described the film fill sheet design parameters. The parameters require dispersing the water over the film fill sheets in a thin film for maximum surface area, retarding the gravitational flow of the water to expose the maximum feasible amount of the water to cooling air, providing turbulent airflow without excessive pressure drop, and resisting mineral and biological clogging. Prior art met these parameters with film fill sheets corrugated in a chevron pattern. However until the present invention, chevron patterns have been viewed as the preeminent surface feature for film fill sheets.
A typical chevron pattern for a film fill sheet is shown in U.S. Pat. No. 4,548,766. The chevrons, point to the side, divide the heated water and form vertical serpentine channels to slow the descent of heated water while increasing surface area. The chevron pattern appears again in the film fill sheet depicted by U.S. Pat. No. 4,809,410 where the chevrons repeat in an alternating manner thus establishing ridgelines and corresponding valleys. The serpentine channels formed by the chevron pattern define the path of the heated water and provide no opportunity for the heated water to change channels except for overtopping the chevron ridgeline.
With edges open for airflow and water passage, film fill sheets may allow cooled water to be ejected from the tower cabinet in the airflow. Ejected cooled water reduces the efficiency of the cooling tower. U.S. Pat. No. 4,801,410 shows side edges with a corrugated pattern to permit airflow while minimizing ejection of cooled water. A corrugated pattern on side edges provides the opportunity for the loss of cooled water, while an edge bar reduces that opportunity.
During operation of a water cooling tower, when film fill sheets are loaded with heated water, the film fill sheets tend to warp or bend. Such deflection of the film fill sheet reduces the cross-sectional area of the adjacent space available for passage of air. The prior art of U.S. Pat. No. 4,548,766 has developed spacers to counter the tendency for the film fill sheet to warp. The spacers reduce the unbraced length of the sheet which stiffens the sheet under heated water loading conditions. A film fill sheet attains required stiffness with spacers regularly located along the perimeter of the sheet and in the vicinity of the center of the sheet.
To maximize cooling, prior art film fill sheets were stacked to form tubular passages that guided the cooling airflow. Building on a chevron pattern, U.S. Pat. No. 4,119,140 assembles tube shaped members to exchange heat with the Atmosphere. Later, U.S. Pat. No. 5,147,583 forms tubular air passages by the cooperation of adjacent film fill sheets. The tubular passages divert the airflow and increase turbulence.
Generally, U.S. Pat. No. 4,826,636 teaches that arrangement of film fill packs effects tower efficiency yet, this patent has little detail on features for a film fill sheet. Also, prior art water cooling towers have required treatment of the cooling water to deter mineral and biological accumulations as in U.S. Pat. No. 5,147,583.
The prior art has met its intended parameters, yet the prior art did not slow the flow of heated water sufficiently to maximize cooling.